This invention relates to optical devices and optical networks.
To route optical signals, an optical network may employ programmable optical add/drop multiplexers (OADM""s) and optical cross connects (OXC""s). OADM""s add optical signals to and drop optical signals from optical trunk lines. OXC""s switch optical signals between different optical trunk lines. OADM""s and OXC""s may perform signal routing without converting optical signals into intermediate electrical signals.
To increase transmission bandwidths, an optical network may also perform wavelength division multiplexing. In wavelength division multiplexing, each optical trunk line can transmit several optical signals simultaneously by transmitting the signals at different wavelengths. In wavelength division multiplexed networks, optical elements select and route optical signals based on wavelength.
In wavelength division multiplexed networks, OADM""s and OXC""s may shift signal wavelengths to enable routing of signals from one optical line to another. Shifting a signal""s wavelength enables a switch to route the signal from one optical line where the signal has one wavelength, to another optical line where the same wavelength is already being used to carry another signal. By shifting signal wavelengths, OADM""s and OXC""s are able to more completely utilize available transmission bandwidth in optical trunk lines of a wavelength division multiplexed network.
In general, in a first aspect, the invention features a process of shifting wavelengths of optical pulses. The process includes transmitting an incoming optical pulse through a nonlinear optical material, splitting the transmitted pulse into a plurality of mutually coherent optical pulses, and recombining the mutually coherent pulses with inter-pulse temporal delays. The recombined pulses produce a temporal interference pattern. The pattern has a peak whose wavelength is shifted with respect to the wavelength of the incoming optical pulse.
Other embodiments of the process include one or more of the following features. One feature is that the transmitting chirps the incoming optical pulse, which may bandwidth enhance the pulse. The chirping may result from self-phase or cross-phase modulation of the pulse. The chirped pulse has about the same temporal width as the incoming optical pulse. Another feature is that the splitting amplitude splits the pulse. Another feature is that the interference pattern be sent to an optical amplitude discriminator.
The chirping may include applying a control optical signal to the nonlinear optical material to set a spectral modulation level for the incoming optical pulse. To apply the control signal, a voltage may be generated across the nonlinear optical material or a light control signal may be sent through the nonlinear optical material. The amplitude splitting may include separating the transmitted pulse into a plurality of pulses and sending each pulse of the plurality to a separate optical conduit. The different conduits have different optical path lengths determined in part by a control signal. The control signal may produce a voltage across or an increased light intensity in a section of one or more of the optical conduits.
In a second aspect, the invention features an apparatus. The apparatus includes a nonlinear optical material capable of chirping optical pulses and a temporal grating generator (TGG) capable of producing a series of mutually coherent optical pulses from a received pulse. The TGG is optically coupled to the nonlinear optical material.
Other embodiments include one or more of the following features. One feature is that the TGG is configured to make pulses of the series overlap. Another feature is that the TGG is a variable TGG that produces several temporal inter-pulse spacings. Another feature is that pulses passing through the TGG and the nonlinear optical material are sent to an amplitude discriminator. Another feature is that the nonlinear optical material is a semiconductor or a low dispersion optical fiber.
The TGG may include an optical amplitude splitter with several output terminals, an optical coupler with several input terminals and optical conduits that connect the output terminals to the input terminals. The optical conduits may have different optical path lengths. One or more of the optical conduits may also have a section whose optical path length is responsive to control signals.
The nonlinear optical material may be coupled to receive optical pulses from the TGG, or the TGG may be coupled to receive optical pulses from the nonlinear optical material.
In a third aspect, the invention features an optical switch. The optical switch includes a wavelength division multiplexer (WDM) and a wavelength shifter to shift a wavelenth of an optical pulse. The wavelength shifter is coupled to transmit the optical pulse with a shifted wavelength to the WDM. The wavelength shifter includes a nonlinear optical material capable of chirping pulses and a temporal grating generator (TGG) optically coupled to the nonlinear optical material.
Other embodiments of the switch may include one or more of the following features. One feature is that the wavelength shifter includes an amplitude discriminator coupled to receive optical pulses from the TGG or the nonlinear optical material. Another feature is that the nonlinear optical material is a semiconductor or a low dispersion optical fiber such as a dispersion decreasing fiber. Another feature is that the switch includes an optical coupler having a plurality of input terminals and an output terminal coupled to the wavelength shifter. Another feature is that the optical coupler is a wavelength division multiplexer. The WDM""s may be coupled for bi-directional transmission. Another feature is that at least one wavelength shifter connects to an output terminal of the WDM.
In a fourth aspect, the invention features a process for routing optical pulses. The process includes shifting a wavelength of an incoming pulse by transmitting the pulse through both a TGG and a nonlinear optical material. The process also includes routing the pulse with a shifted wavelength to one of a plurality of optical output lines based on the shifted wavelength.
Other embodiments may include one or more of the following features. One feature is that the shifting transmits the incoming pulse through the nonlinear optical medium to chirp the pulse and then sends the chirped pulse through a TGG. Another feature is that the shifting sends the incoming pulse through a TGG to produce a series of mutually coherent pulses and then transmit the series through a nonlinear optical medium to chirp the pulses in the series. Another feature is that the process further shifts the wavelengths of the routed the pulse to another wavelength in response to routing the pulse to an optical output line having an available transmission channel at the other wavelength.
In a fifth aspect, the invention features a process that shifts wavelengths of optical pulses. The process includes splitting an incoming optical pulse into a plurality of mutually coherent optical pulses and recombining the mutually coherent optical pulses through a nonlinear optical material to produce a temporal interference pattern having a peak whose wavelength is shifted with respect to the wavelength of the incoming optical pulse.
Other embodiments include one or more of the following features. One feature is that the transmitting chirps each pulse of the series. Another feature is that the transmitting bandwidth enhances each pulse of the series. Another feature is that the transmitting includes performing one of sel-phase modulation and cross-phase modulation on the pulses of the series. Another feature is that the splitting amplitude splits the incoming pulse into a plurality of pulses and sends each pulse of the plurality to a separate optical conduit. Different ones of the optical conduits have different optical path lengths.
Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.